Scanning device

ABSTRACT

A scanning device includes an MEMS mirror mechanism that swings a mirror with respect to a first axial line as a central line and swings the mirror with respect to a second axial line as a central line, and a control unit that generates a first drive signal for swinging the mirror with respect to the first axial line, and a second drive signal for swinging the mirror with respect to the second axial line. The control unit generates the first drive signal and the second drive signal so that m times of reciprocation of an irradiation region in a first direction and one time of reciprocation of the irradiation region in a second direction correspond to each other by repeating generation of a second signal element constituting the second drive signal to correspond to a first signal element in a period equal to or less than one cycle in the first drive signal.

TECHNICAL FIELD

The present disclosure relates to a scanning device.

BACKGROUND ART

As a scanning device, for example, a scanning device that performsscanning with laser light by using a MEMS (micro electro mechanicalsystems) mirror mechanism to display an image is known. In the scanningdevice, for example, an image of one frame or two frames is formed by mtimes of reciprocation (m: an integer of two or greater) of anirradiation region of laser light in a horizontal direction, and onetime of reciprocation of the irradiation region of the laser light in avertical direction. Patent Literature 1 discloses a technology in whichsynchronization is performed at the time of initiating one frame and atthe time of terminating one frame between a horizontal drive signal anda vertical drive signal for driving the MEMS mirror mechanism.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No.2006-276634

SUMMARY OF INVENTION Technical Problem

However, for example, in a case where a mirror is caused to be resonatedby the horizontal drive signal, when a resonance frequency of the mirrorvaries in one frame due to a variation of an ambient temperature or thelike, in the technology described in Patent Literature 1, it isdifficult to correct a deviation that occurs in a correspondingrelationship between the horizontal drive signal and the vertical drivesignal until the one frame is terminated, and as a result, there is aconcern that display of an image may be unstable.

An object of the present disclosure is to provide a scanning devicecapable of realizing stable scanning with laser light.

Solution to Problem

A scanning device according to an aspect of the present disclosureincludes: a light source that emits laser light; an MEMS mirrormechanism that includes a mirror that reflects the laser light emittedfrom the light source, reciprocates an irradiation region of the laserlight in a first direction by swinging the mirror with respect to afirst axial line as a central line, and reciprocates the irradiationregion in a second direction that intersects the first direction byswinging the mirror with respect to a second axial line as a centralline that intersects the first axial line; and a control unit thatgenerates a first drive signal for swinging the mirror with respect tothe first axial line as a central line and a second drive signal forswinging the mirror with respect to the second axial line as a centralline, and inputs the first drive signal and the second drive signal tothe MEMS mirror mechanism. The first drive signal is an electric signalin which one swing of the mirror with respect to the first axial line asa central line is set as one cycle, the second drive signal is anelectric signal in which one swing of the mirror with respect to thesecond axial line as a central line is set as one cycle, and the controlunit generates a second signal element constituting the second drivesignal to correspond to a first signal element in a period equal to orless than one cycle period in the first drive signal, and repeatsgeneration of the second signal element in both an outgoing period andan incoming period in the one swing of the mirror with respect to thesecond axial line as a central line to generate the first drive signaland the second drive signal so that m times of reciprocation (m: aninteger of two or greater) of the irradiation region in the firstdirection and one time of reciprocation of the irradiation region in thesecond direction correspond to each other.

In the scanning device, the second signal element constituting thesecond drive signal is generated to correspond to the first signalelement in a period equal to or less than one cycle period in the firstdrive signal. In addition, generation of the second signal element isrepeated in both an outgoing period and an incoming period in the oneswing of the mirror with respect to the second axial line as a centralline. According to this, even when the MEMS mirror mechanism isinfluenced by a variation of an ambient temperature or the like, it ispossible to suppress occurrence of a deviation in a correspondingrelationship between the first drive signal and the second drive signal.Accordingly, according to the scanning device, stable scanning withlaser light becomes possible.

In the scanning device according to the aspect of the presentdisclosure, the first drive signal may be an electric signal forresonating the mirror with respect to the first axial line as a centralline, the second drive signal may be an electric signal for linearlyoperating the mirror with respect to the second axial line as a centralline, and the control unit may modulate a frequency of the first drivesignal to conform to a resonance frequency of the mirror. According tothis, even when the resonance frequency of the mirror varies due to avariation of an ambient temperature or the like, it is possible to morereliably suppress occurrence of a deviation in a correspondingrelationship between the first drive signal and the second drive signal.

In the scanning device according to the aspect of the presentdisclosure, the control unit may control the light source so that theoutgoing period corresponds to a lighting-on period and the incomingperiod corresponds to a lighting-off period, and may repeat generationof the second signal element in the both lighting-on period and thelighting-off period. According to this, it is possible to suppressoccurrence of a deviation in a corresponding relationship between thefirst drive signal and the second drive signal in the respectivelighting-on periods. Note that, the lighting-on period is a period inwhich the control unit causes the light source to emit laser light, andthe lighting-off period is a period in which the control unit does notcause the light source to emit the laser light.

In the scanning device according to the aspect of the presentdisclosure, the control unit may control the light source so that theoutgoing period corresponds to a first lighting-on period and theincoming period corresponds to a second lighting-on period, and mayrepeat generation of the second signal element in both the firstlighting-on period and the second lighting-on period. According to this,it is possible to suppress occurrence of the deviation in thecorresponding relationship between the first drive signal and the seconddrive signal in the first lighting-on period and the second lighting-onperiod. Note that, the first lighting-on period and the secondlighting-on period are periods in which the control unit causes thelight source to emit laser light.

In the scanning device according to the aspect of the presentdisclosure, the control unit may generate the second signal element tocorrespond to the first signal element in a ½ cycle period in the firstdrive signal. Alternatively, the control unit may generate the secondsignal element to correspond to the first signal element in a one cycleperiod in the first drive signal. According to this, it is possible tomake a process when generating the second signal element easy.

In the scanning device according to the aspect of the presentdisclosure, the control unit may generate the second signal element tocorrespond to the first signal element in a current one cycle period inthe first drive signal. Alternatively, the control unit may generate thesecond signal element to correspond to the first signal element in animmediately previous one cycle period in the first drive signal.According to this, time delay when generating the second signal elementcan be minimized.

In the scanning device according to the aspect of the presentdisclosure, the MEMS mirror mechanism may include a first movable unitprovided with the mirror, a second movable unit that supports the firstmovable unit to be swingable with respect to the first axial line as acentral line, a support unit that supports the second movable unit to beswingable with respect to the second axial line as a central line, adrive coil that is provided in the second movable unit, and a magnetthat generates a magnetic field acting on the drive coil. Theelectromagnetic drive type MEMS mirror mechanism is susceptible to avariation of an ambient temperature or the like, and thus repetition ofgeneration of the second signal element as described above isparticularly effective.

In the scanning device according to the aspect of the presentdisclosure, the light source may emit the laser light for projectiondisplay, and the control unit may generate the first drive signal andthe second drive signal so that an image of one frame or two frames isformed by the m times of reciprocation of the irradiation region in thefirst direction and the one time of reciprocation of the irradiationregion in the second direction. As described above, it is possible tosuppress occurrence of a deviation in the corresponding relationshipbetween the first drive signal and the second drive signal, and thus, inthis case, stable image display is possible.

In the scanning device according to the aspect of the presentdisclosure, the control unit may control the light source so that thelaser light is modulated in correspondence with a position of theirradiation region. According to this, image display with higher qualityis possible.

In the scanning device according to the aspect of the presentdisclosure, the control unit may repeat generation of the second signalelement while fluctuating a frame rate. According to this, it ispossible to easily and reliably repeat generation of the second signalelement.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide ascanning device capable of realizing stable scanning with laser light.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a scanning display system providedwith a scanning device according to a first embodiment.

FIG. 2 is a configuration diagram of a MEMS mirror mechanism and acontrol unit of the scanning device illustrated in FIG. 1 .

FIG. 3 is a view illustrating a scanning trajectory of laser light on aprimary image plane of the scanning device illustrated in FIG. 1 .

FIG. 4 is a view illustrating a relationship between a first drivesignal and a second drive signal in the scanning device illustrated inFIG. 1 .

FIG. 5 is an enlarged view illustrating a relationship between the firstdrive signal and the second drive signal in the scanning deviceillustrated in FIG. 1 .

FIG. 6 is a view illustrating a relationship between the first drivesignal and the second drive signal in the scanning device illustrated inFIG. 1 .

FIG. 7 is a view illustrating a relationship between a first drivesignal and a second drive signal in a scanning device of a comparativeexample.

FIG. 8 is a configuration diagram of a modification example of the MEMSmirror mechanism and the control unit.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present disclosure will be describedin detail with reference to the accompanying drawings. Note that, thesame reference numeral will be given to the same or correspondingportion in respective drawings, and redundant description will beomitted.

[Configuration of Scanning Device]

As illustrated in FIG. 1 , for example, a scanning display system 10 isa laser scanning projection display that is mounted on a vehicle, anddisplays (projects and displays) an image to a windshield 100 of thevehicle. The scanning display system 10 includes a scanning device 1 andan optical system 11. The optical system 11 includes a plurality ofplanar mirrors 11 a and 11 b, a concave mirror 11 c, and a windshield100. The windshield 100 functions as an optical element on a rearmoststage in the optical system 11. Light L2 for projection display which isemitted from the scanning device 1 is sequentially reflected by theplanar mirror 11 a, the planar mirror 11 b, the concave mirror 11 c, andthe windshield 100, and is incident to an eye E of an observer.

The scanning device 1 includes a light source 2, a MEMS mirror mechanism3, a light diffusion unit 4, and a control unit 5. The light source 2emits laser light L1 for projection display. More specifically, thelight source 2 includes a plurality of light emission units 2 a. Forexample, the plurality of light emission units 2 a are a red laserdiode, a green laser diode, and a blue laser diode, respectively. Thelight emission units 2 a emits the laser light L1 having a wavelength ina visible region. The laser light L1 emitted from the light emissionunits 2 a is reflected by a plurality of mirrors 2 b including adichroic mirror, proceeds on the same light path, and is incident to theMEMS mirror mechanism 3.

The MEMS mirror mechanism 3 includes a mirror 3 a that reflects thelaser light L1 emitted from the light source 2. The MEMS mirrormechanism 3 is a drive mirror manufactured by a MEMS (micro electromechanical systems) technology, and a drive type of the MEMS mirrormechanism 3 is an electromagnetic drive type (details thereof will bedescribed later). The MEMS mirror mechanism 3 scans the light diffusionunit 4 with the laser light L1 by swinging the mirror 3 a with respectto a first axial line and a second axial line which are orthogonal toeach other as a central line.

The light diffusion unit 4 diffuses the laser light L1 in the scanningby the MEMS mirror mechanism 3. For example, the light diffusion unit 4is a transmission-type microlens array, and allows the laser light L1 inthe scanning by the MEMS mirror mechanism 3 to be transmitted anddiffuses the laser light L1. In the laser light L1 diffused by the lightdiffusion unit 4, light constituting an image is incident to the opticalsystem 11 disposed on a rear stage of the light diffusion unit 4 aslight L2 for projection display.

The control unit 5 controls the light source 2 and the MEMS mirrormechanism 3. As an example, when receiving an input signal indicatinginitiation of projection display, the control unit 5 initiates output ofthe light emission units 2 a of the light source 2. According to this,the laser light L1 is emitted from the light source 2. At substantiallythe same time, the control unit 5 initiates an operation of the MEMSmirror mechanism 3. According to this, in the MEMS mirror mechanism 3,swinging of the mirror 3 a is initiated, and the light diffusion unit 4is scanned with the laser light L1 emitted from the light source 2. Atthis time, the control unit 5 changes a ratio of the laser light L1emitted from each of the respective light emission units 2 a incorrespondence with a scanning position of the laser light L1 (aposition of an irradiation region with the laser light L1) in the lightdiffusion unit 4. According to this, light L2 for projection display(that is, light constituting an image in the laser light L1 diffused bythe light diffusion unit 4) is sequentially reflected by the planarmirror 11 a, the planar mirror 11 b, the concave mirror 11 c, and thewindshield 100, and is incident to the eye E of the observer.

[Configuration of MEMS Mirror Mechanism]

As illustrated in FIG. 2 , the MEMS mirror mechanism 3 includes a firstmovable unit 31, a second movable unit 32, a support unit 33, a firstdrive coil 34, a second drive coil (drive coil) 35, and a magnet 37 inaddition to the mirror 3 a. The mirror 3 a is provided in the firstmovable unit 31. The second movable unit 32 supports the first movableunit 31 to be swingable with respect to a first axial line A1 as acentral line. The support unit 33 supports the second movable unit 32 tobe swingable with respect to a second axial line A2 that intersects(here, that is orthogonal to) the first axial line A1 as a central line.

More specifically, the second movable unit 32 is formed in a frame shapeto surround the first movable unit 31, and is connected to the firstmovable unit 31 through a pair of torsion bars 38 disposed on the firstaxial line A1. The support unit 33 is formed in a frame shape tosurround the second movable unit 32, and is connected to the secondmovable unit 32 through a pair of torsion bars 39 disposed on the secondaxial line A2. The first movable unit 31, the second movable unit 32,the support unit 33, the pair of torsion bars 38, and the pair oftorsion bars 39 are integrally formed, for example, by an SOI (siliconon insulator) substrate.

The first drive coil 34 is provided in the first movable unit 31. Afirst drive signal S1 for swinging the mirror 3 a with respect to thefirst axial line A1 as a central line is input to the first drive coil34 from the control unit 5, and an electromotive force signal S3 isoutput to the control unit 5 from the first drive coil 34. The seconddrive coil 35 is provided in the second movable unit 32. A second drivesignal S2 for swinging the mirror 3 a with respect to the second axialline A2 as a central line is input to the second drive coil 35 from thecontrol unit 5. The magnet 37 generates a magnetic field acting on thefirst drive coil 34 and the second drive coil 35.

The first drive signal S1 is an electric signal that resonates themirror 3 a with respect to the first axial line A1 as a central line.When the first drive signal S1 is input to the first drive coil 34, aLorenz force acts on the first drive coil 34 due to a mutual operationwith the magnetic field generated by the magnet 37. In addition to theLorenz force, when using resonance of the mirror 3 a and the firstmovable unit 31 in a natural frequency, it is possible to resonate themirror 3 a with respect to the first axial line A1 as a central line.Note that, the natural frequency is determined by a mass of the mirror 3a and the first movable unit 31, a spring constant of the pair oftorsion bars 38, and the like.

The second drive signal S2 is an electric signal for linearly operatingthe mirror 3 a with respect to the second axial line A2 as a centralline. When the second drive signal S2 is input to the second drive coil35, a Lorenz force acts on the second drive coil 35 due to a mutualoperation with the magnetic field that is generated by the magnet 37. Itis possible to linearly operate the mirror 3 a with respect to thesecond axial line A2 as a central line by using balance between theLorenz force and an elastic force of the pair of torsion bars 39.

The electromotive force signal S3 is an electric signal for acquiringinformation relating to a vibration angle of the mirror 3 a or the like.When the first movable unit 31 is swung in the magnetic field generatedby the magnet 37, an electromotive force is generated in the first drivecoil 34 provided in the first movable unit 31. The electromotive forcecorresponds to the electromotive force signal S3.

[Relationship Between First and Second Drive Signals and Frame]

As illustrated in FIG. 2 and FIG. 3 , the MEMS mirror mechanism 3reciprocate an irradiation region of the laser light L in a horizontaldirection (first direction) D1 by swinging the mirror 3 a with respectto the first axial line A1 as a central line, and reciprocate theirradiation region of the laser light L in a vertical direction (seconddirection that intersects the first direction) D2 by swinging the mirror3 a with respect to the second axial line A2 as a central line. Thecontrol unit 5 generates the first drive signal S1 and the second drivesignal S2 so that an image of one frame is formed by m times ofreciprocation (m: an integer of two or greater) of the irradiationregion of the laser light L1 in the horizontal direction D1 and one timeof reciprocation of the irradiation region of the laser light L1 in thevertical direction D2.

Note that, FIG. 3 is a view illustrating a scanning trajectory of thelaser light L1 on a primary image plane (here, a predetermined region inthe light diffusion unit 4). In FIG. 3 , a solid-line trajectoryrepresents the scanning trajectory of the laser light L1 emitted fromthe light source 2. A broken-line trajectory represents a scanningtrajectory of the laser light L1 in a case where the laser light L1 isnot actually emitted from the light source 2, but the laser light L1 isassumed to be emitted. That is, in the scanning device 1, an image isformed by performing scanning with the laser light L1 so that a drawingperiod (lighting-on period: a period in which the control unit 5 causesthe light source 2 to emit the laser light L1) and a returning period(lighting-off period: a period in which the control unit 5 does notcause the light source 2 to emit the laser light L1) are provided(details will be described later).

As illustrated in FIG. 4 , the first drive signal S1 is a rectangularwave in which one swing of the mirror 3 a with respect to the firstaxial line A1 as a central line is set as one cycle T1. The second drivesignal S2 is a triangular wave in which one swing of the mirror 3 a withrespect to the second axial line A2 as a central line is set as onecycle T2. In the second drive signal S2, in the one swing of the mirror3 a with respect to the second axial line A2 as a central line, anoutgoing period T2 a in which the mirror 3 a rotates in one direction islonger than an incoming period T2 b in which the mirror 3 a rotates in adirection opposite to the one direction.

The outgoing period T2 a of the second drive signal S2 corresponds to aperiod obtained by accumulating the one cycle T1 of the first drivesignal S1 n times (n: an integer of two or greater). The laser light L1is emitted from the light source 2 during the outgoing period T2 a. Thatis, the outgoing period T2 a is a drawing period in which the laserlight L1 is emitted from the light source 2. The incoming period T2 b ofthe second drive signal S2 corresponds to a period obtained byaccumulating the one cycle T1 of the first drive signal S1 m-n times(m-n: an integer of one or greater and smaller than n (here, an integerof two or greater and smaller than n)). The laser light L is not emittedfrom the light source 2 during the incoming period T2 b. That is, theincoming period T2 b is a returning period for which the laser light L1is not emitted from the light source 2. Note that, the scanningtrajectory of the laser light L1 as illustrated in FIG. 3 is an exampleof a case where a relationship between the first drive signal S1 and thesecond drive signal S2 as illustrated in FIG. 4 is further simplified.

[Configuration of Control Unit]

As illustrated in FIG. 2 , the control unit 5 includes a PLL (phaselocked loop) circuit 51. The PLL circuit 51 includes a phase comparator51 a, a loop filter 51 b, and a VCO (voltage controlled oscillator) 51c. The electromotive force signal S3 superimposed on the first drivesignal S1 is input to the phase comparator 51 a from the first drivecoil 34. The phase comparator 51 a changes a voltage in correspondencewith a variation of a phase of the electromotive force signal S3, andoutputs a signal in which a voltage is changed. The loop filter 51 bremoves a high-frequency component from the signal in which the voltageis changed by the phase comparator 51 a, and outputs the signal fromwhich the high-frequency component is removed. The VCO 51 c changes afrequency in correspondence with a variation of a voltage in the signalfrom which the high-frequency component is removed by the loop filter 51b, and outputs the signal in which the frequency is changed.

The control unit 5 further includes a frequency divider 52, a D/Aconverter 53, and constant current circuits 57 and 58. The frequencydivider 52 divides a frequency of the signal in which the frequency ischanged by the VCO 51 c, and inputs the frequency-divided signal to thefirst drive coil 34 as the first drive signal S1. At this time, thefirst drive signal S1 is converted into a current by the constantcurrent circuit 57. The D/A converter 53 generates the second drivesignal S2 on the basis of the signal in which the frequency is dividedby the frequency divider 52, and inputs the generated second drivesignal S2 to the second drive coil 35. At this time, the second drivesignal S2 is converted into a current by the constant current circuit58. In the MEMS mirror mechanism 3, a resonance frequency of the mirror3 a may vary due to a variation of an ambient temperature or the like.When the resonance frequency of the mirror 3 a varies, a phase of theelectromotive force signal S3 varies. Accordingly, the control unit 5can modulate the frequency of the first drive signal S1 to conform tothe resonance frequency of the mirror 3 a by operating the PLL circuit51 and the frequency divider 52 as described above.

The control unit 5 further includes a memory 54, a timing signalgeneration unit 55, and an LD driver 56. The memory 54 stores imageinformation for projection display. The timing signal generation unit 55reads out image information corresponding to a scanning position of thelaser light L1 on the basis of the signal in which the frequency isdivided by the frequency divider 52 from the memory 54, and transmitsthe read-out image information to the LD driver 56. The LD driver 56controls the light source 2 so that the laser light L1 is modulated incorrespondence with a scanning position of the laser light L1 (that is,so that a ratio of the laser light L1 emitted from each of the lightemission units 2 a varies in correspondence with the scanning positionof the laser light L1).

Generation of the first drive signal S1 and the second drive signal S2by the control unit 5 will be described in more detail. As illustratedin FIG. 5 , the control unit 5 generates a second signal element S2 _(i)constituting the second drive signal S2 to correspond to a first signalelement S1 _(i) in a current one cycle T1 in the first drive signal S1.More specifically, the control unit 5 generates the second signalelement S2 _(i) constituting the second drive signal S2 corresponding toone cycle T1 to correspond to the first signal element S1 _(i) of ½cycle in the current one cycle T1 in the first drive signal S1. Here,the control unit 5 sets the period of the first signal element S1 _(i)to be a period conforming to the resonance frequency of the mirror 3 aon the basis of a variation of the phase of the electromotive forcesignal S3 with respect to the first signal element S1 _(i). According tothis, the control unit 5 sets a period of the second signal element S2_(i) to correspond to the first signal element S1 _(i), and sets avoltage value of the second signal element S2 _(i).

The control unit 5 may generate the second signal element S2 _(i)constituting the second drive signal S2 to correspond to a first signalelement S1 _(i-1) in an immediately previous one cycle T1 (one cycle T1before the current one cycle T1 by one cycle) in the first drive signalS1. More specifically, the control unit 5 generates the first signalelement S1 _(i) of ½ cycle in the current one cycle T1 in the firstdrive signal S1 corresponding to one cycle T1 on the basis of the firstsignal element S1 _(i-1) of ½ cycle in the immediately previous onecycle T1 (may be the first signal element S1 _(i-1) of the first-half ½cycle in the immediately previous one cycle T1, or may be the firstsignal element S1 _(i-1) of the second-half ½ cycle in the immediatelyprevious one cycle T1) in the first drive signal S1. Here, the controlunit 5 sets the period of the first signal element S1 _(i) to be aperiod conforming to the resonance frequency of the mirror 3 a on thebasis of a variation of a phase of the electromotive force signal S3with respect to the first signal element S1 _(i-1). According to this,the control unit 5 generates the second signal element S2 _(i)constituting the second drive signal S2 corresponding to one cycle T1 tocorrespond to the first signal element S1 _(i). Here, the control unit 5sets a period of the second signal element S2 _(i) to be the same periodas in the first signal element S1 _(i), and sets a voltage value of thesecond signal element S2 _(i).

Note that, the control unit 5 generates the second signal element S2_(i) to correspond to the first signal element S1 _(i) or S1 _(i-1) in a½ cycle period in the first drive signal S1, but may generate the secondsignal element S2 _(i) to correspond to the first signal element S1 _(i)or S1 _(i-1) in an one cycle period in the first drive signal S1. Thecontrol unit 5 can generate the second signal element S2 _(i) tocorrespond to the first signal element S1 _(i) or S1 _(i-1) in a periodequal to or less than one cycle in the first drive signal S1.

The control unit 5 repeats generation of the first signal element S1 iand generation of the second signal element S2 i as described above inboth the drawing period and the returning period while controlling thelight source 2 (refer to FIG. 4 ) so that the outgoing period T2 acorresponds to the drawing period and the incoming period T2 bcorresponds to the returning period. According to this, in a case wherethe period of the first signal element S1 i is constant as illustratedin the upper part of FIG. 6 , and in a case where the period of thefirst signal element S1 i varies in one frame due to a variation of theresonance frequency of the mirror 3 a as illustrated in in the lowerpart of FIG. 6 , a deviation does not occur in the correspondingrelationship between the first drive signal S1 and the second drivesignal S2. As described above, the control unit 5 repeats generation ofthe first signal element S1 i and the second signal element S2 i whilefluctuating a frame rate (the number of frames processed per unit time).

If generation of the first signal element S1 i and generation of thesecond signal element S2 _(i) are not repeated in both the drawingperiod and the returning period, in a case where the period of the firstsignal element S1 i is constant as illustrated in the upper part of FIG.7 , a deviation does not occur in the corresponding relationship betweenthe first drive signal S1 and the second drive signal S2, but in a casewhere the period of the first signal element S1 i varies in one framedue to the variation of the resonance frequency of the mirror 3 a asillustrated in the lower part of FIG. 7 , a deviation occurs in thecorresponding relationship between the first drive signal S1 and thesecond drive signal S2.

[Operation and Effect]

In the scanning device 1, the first drive signal S1 and the second drivesignal S2 are generated so that m times of reciprocation (m: an integerof two or greater) of the irradiation region of the laser light L1 inthe horizontal direction and one time of reciprocation of theirradiation region of the laser light L1 in the vertical directioncorrespond to each other. More specifically, the second signal elementS2 _(i) constituting the second drive signal S2 is generated tocorrespond to the first signal element S1 _(i) in a period equal to orless than one cycle period in the first drive signal S1. In addition,generation of the second signal element S2 _(i) is repeated in both theoutgoing period T2 a and the incoming period T2 b in the one swing ofthe mirror 3 a with respect to the second axial line A2 as a centralline. According to this, even though the MEMS mirror mechanism 3 isinfluenced by a variation of an ambient temperature or the like, it ispossible to suppress occurrence of a deviation in the correspondingrelationship between the first drive signal S1 and the second drivesignal S2. Accordingly, according to the scanning device 1, stablescanning with the laser light L1, and further, stable image display (forexample, image display in which occurrence of a flicker phenomenon thatoccurs in a case as illustrated in the upper part of FIG. 7 issuppressed) become possible.

As described above, in a case where the control unit 5 generates thesecond signal element S2 _(i) to correspond to the first signal elementS1 _(i) or S1 _(i-1) in a ½ cycle period in the first drive signal S1,or in a case where the control unit 5 generates the second signalelement S2 _(i) to correspond to the first signal element S1 _(i) or S1_(i-1) in an one cycle period in the first drive signal S1, it ispossible to make a process when generating the second signal element S2_(i) easy. In addition, in a case where the control unit 5 generates thesecond signal element S2 _(i) to correspond to the first signal elementS1 _(i) in a current one cycle T1 in the first drive signal S1, or in acase where the control unit 5 generates the second signal element S2_(i) to correspond to the first signal element S1 _(i-1) in animmediately previous one cycle T1 in the first drive signal S1, timedelay when generating the second signal element S2 _(i) can beminimized. In addition, in a case where the control unit 5 generates thesecond signal element S2 _(i) to correspond to the first signal elementS1 _(i) in the current one cycle T1 in the first drive signal S1, evenwhen the resonance frequency of the mirror 3 a varies in the middle ofthe first signal element S1 _(i) and the period of the first signalelement S1 _(i) is shortened, it is possible to make the period of thesecond signal element S2 _(i) match the period of the first signalelement S1 _(i) by determining the period of the second signal elementS2 _(i) with reference to the electromotive force signal S3corresponding to the first signal element S1 _(i).

In the scanning device 1, the first drive signal S1 is an electricsignal for resonating the mirror 3 a with respect to the first axialline A1 as a central line, the second drive signal S2 is an electricsignal for linearly operating the mirror 3 a with respect to the secondaxial line A2 as a central line, and the control unit 5 modulates thefrequency of the first drive signal S1 to conform to the resonancefrequency of the mirror 3 a. According to this, even when the resonancefrequency of the mirror 3 a varies due to a variation of an ambienttemperature or the like, it is possible to more reliably suppressoccurrence of a deviation in the corresponding relationship between thefirst drive signal S1 and the second drive signal S2. Particularly, inthe control unit 5, since the PLL circuit 51 is used, it is notnecessary to separately provide a configuration for measuring theresonance frequency of the mirror 3 a, and thus it is possible torealize reduction in size of the device and simplification of aconfiguration of the device.

In the scanning device 1, the control unit 5 controls the light source 2so that the outgoing period T2 a corresponds to the drawing period andthe incoming period T2 b corresponds to the returning period, andrepeats generation of the second signal element S2 _(i) in both thedrawing period and the returning period. In a case where the returningperiod is provided in the scanning with the laser light L1, since atemperature of the MEMS mirror mechanism 3 is lowered in the returningperiod in which the mirror 3 a is not irradiated with the laser lightL1, the resonance frequency of the mirror 3 a is likely to fluctuate.Accordingly, in a case where the returning period is provided in thescanning with the laser light L1, repeating generation of the secondsignal element S2 _(i) as described above is particularly effective forsuppressing occurrence of a deviation in the corresponding relationshipbetween the first drive signal S1 and the second drive signal S2 in eachdrawing period. That is, since the first drive signal S1 and the seconddrive signal S2 correspond to each other even in the returning period,it is not necessary to adjust the deviation between the first drivesignal S1 and the second drive signal S2 at the time of initiating thesubsequent drawing period. In addition, when stopping the resonanceoperation of the mirror 3 a in the returning period, it is difficult topromptly swing the mirror 3 a at a high speed at the time of initiatingthe subsequent drawing period, and as a result, an image is blurred atthe time of initiating the subsequent drawing period. In the scanningdevice 1, since the resonance operation of the mirror 3 a is not stoppedby providing the first drive signal S1 corresponding to a plurality ofcycles in the returning period, the resonance operation of the mirror 3a becomes stable at the time of initiating the subsequent drawingperiod, and an image is not blurred at the time of initiating thesubsequent drawing period.

In the scanning device 1, the electromagnetic drive type MEMS mirrormechanism 3 is used. In the electromagnetic drive type MEMS mirrormechanism 3, the resonance frequency of the mirror 3 a is likely to varydue to a variation of a spring constant of the pair of torsion bars 38due to a variation of an ambient temperature, a variation of a moment ofinertia due to attachment of particles or the like, a variation of anattenuation coefficient of the pair of torsion bars 38 due to avariation of an atmospheric pressure, a variation of the spring constantof the pair of torsion bars 38 due to an operation of the second movableunit 32 with respect to the second axial line A2 as a central line, avariation of the spring constant and the attenuation coefficient of thepair of torsion bars 38 due to an aging variation of metal wiresprovided in the pair of torsion bars 38, or the like. The size of theMEMS mirror mechanism 3 is small, and thus fluctuation of the resonancefrequency of the mirror 3 a is more significant in comparison to alarge-sized mirror mechanism such as a galvano mirror. Accordingly, in acase where the electromagnetic drive type MEMS mirror mechanism 3 isused, repeating generation of the second signal element S2 _(i) asdescribed above is particularly effective for suppressing occurrence ofa deviation in the corresponding relationship between the first drivesignal S1 and the second drive signal S2 in each drawing period.

In the scanning device 1, the control unit 5 controls the light source 2so that the laser light L1 is modulated in correspondence with ascanning position of the laser light L1. According to this, imagedisplay with higher quality is possible. Note that, when an absorptionrate of the laser light L1 in the mirror 3 a fluctuates due tomodulation of the laser light L1, the resonance frequency of the mirror3 a fluctuates. Accordingly, in this case, repeating generating of thesecond signal element S2 _(i) as described above is particularlyeffective for suppressing occurrence of a deviation in the correspondingrelationship between the first drive signal S1 and the second drivesignal S2 in each drawing period.

In the scanning device 1, the control unit 5 repeats generation of thesecond signal element S2 _(i) while fluctuating the frame rate.According to this, it is possible to easily and reliably repeatgeneration of the second signal element S2 _(i). This is a finding foundindependently from a finding in the related art in which the frame rateis typically fixed, and enables stable image display.

Modification Example

The present disclosure is not limited to the one embodiment. Forexample, the light source 2 is not limited to a light source that uses alaser diode (semiconductor laser), and may be a light source that uses asurface-emitting laser, an SLD (super luminescent diode), or the like.In addition, a drive type of the MEMS mirror mechanism 3 is not limitedto the electromagnetic drive type, and may be an electrostatic drivetype, a piezoelectric drive type, a thermal drive type, or the like. Inaddition, the light diffusion unit 4 is not limited to the transmissiontype microlens array, and may be reflection type microlens array, amicro mirror array, a diffraction lattice, a fiber optic plate, or thelike.

In addition, as illustrated in FIG. 8 , the MEMS mirror mechanism 3 mayfurther include an electromotive force monitoring coil 36. Theelectromotive force monitoring coil 36 is provided in the first movableunit 31 to be located on an inner side of the first drive coil 34. Theelectromotive force signal S3 is output to the control unit 5 (morespecifically, the phase comparator 51 a of the PLL circuit 51) from theelectromotive force monitoring coil 36. When the first movable unit 31is swung in the magnetic field generated by the magnet 37, anelectromotive force is generated in the electromotive force monitoringcoil 36 provided in the first movable unit 31. The electromotive forcecorresponds to the electromotive force signal S3. Even in this case,generation of any of the second signal element S2 _(i) is possible.

However, in the case of acquiring the electromotive force generated inthe first drive coil 34 as the electromotive force signal S3, thefollowing advantage is attained. That is, the first drive coil 34 iswound along an outer edge of the first movable unit 31 to swing thefirst movable unit 31 with high efficiency. In this case, a windingdiameter of the first drive coil 34 increases, and thus a largeelectromotive force can be obtained even in a small number of turns. Inaddition, only a wire electrically connected to the first drive coil 34passes through the torsion bars 38, and thus manufacturing of the MEMSmirror mechanism 3 can become easy.

In the MEMS mirror mechanism 3 illustrated in FIG. 2 and FIG. 8 , thefirst drive coil 34 for swinging the first movable unit 31 is providedin the first movable unit 31 and the second drive coil 35 for swingingthe second movable unit 32 is provided in the second movable unit 32,but the MEMS mirror mechanism 3 may be configured as follows. As an MEMSmirror mechanism 3 of a first modification example, a drive coil forswinging the first movable unit 31 and a drive coil for swinging thesecond movable unit 32 may be provided in the second movable unit 32.Alternatively, as an MEMS mirror mechanism 3 of a second modificationexample, a single drive coil for swinging the first movable unit 31 andthe second movable unit 32 may be provided in the second movable unit32.

In the MEMS mirror mechanism 3 of the first modification example and theMEMS mirror mechanism 3 of the second modification example, theelectromotive force monitoring coil may be provided in the first movableunit 31, and in this case, the electromotive force signal S3corresponding to an electromotive force corresponding to swinging of thefirst movable unit 31 may be output to the control unit 5 from theelectromotive force monitoring coil. Alternatively, in the MEMS mirrormechanism 3 of the first modification example and the MEMS mirrormechanism 3 of the second modification example, the electromotive forcemonitoring coil may be provided in the second movable unit 32, and inthis case, the electromotive force signal S3 corresponding to anelectromotive force corresponding to swinging of the first movable unit31 may be output to the control unit 5 from the electromotive forcemonitoring coil. In the MEMS mirror mechanism 3 of the firstmodification example and the MEMS mirror mechanism 3 of the secondmodification example, since the second movable unit 32 is vibrated bythe drive coil provided in the second movable unit 32, and the vibrationis transmitted to the first movable unit 31 to swing the first movableunit 31, even in a case where the electromotive force monitoring coil isprovided in the second movable unit 32, it is possible to measure anelectromotive force corresponding to the swinging of the first movableunit 31. Alternatively, in the MEMS mirror mechanism 3 of the firstmodification example and the MEMS mirror mechanism 3 of the secondmodification example, the electromotive force signal S3 corresponding toan electromotive force generated in the drive coil (that is, the drivecoil provided in the second movable unit 32) in correspondence withswinging of the first movable unit 31 may be output to the control unit5 from the drive coil.

In addition, the control unit 5 may control the light source 2 so thatthe outgoing period T2 a corresponds to a first drawing period (a firstlighting-on period: a period in which the control unit 5 causes thelight source 2 to emit the laser light L1), and the incoming period T2 bcorresponds to a second drawing period (a second lighting-on period: aperiod in which the control unit 5 causes the light source 2 to emit thelaser light L1), and may repeat generation of the second signal elementS2 _(i) in both the first drawing period and the second drawing period.According to this configuration, in the first drawing period and thesecond drawing period, it is possible to suppress occurrence of adeviation in the corresponding relationship between the first drivesignal S1 and the second drive signal S2. Note that, in this case, animage of two frames is formed by m times of reciprocation (m: an integerof two or greater) of an irradiation region of the laser light L1 in thehorizontal direction, and one time of reciprocation of the irradiationregion of the laser light L1 in a vertical direction. In addition, thesecond drive signal S2 in this case, for example, is a triangular wavein which the outgoing period T2 a and the incoming period T2 b aremutually equal to each other.

In addition, the first drive signal S1 may be a sinusoidal wave or thelike without limitation to the rectangular wave as long as the firstdrive signal S1 is an electric signal in which one swing of the mirror 3a with respect to the first axial line A1 as a central line is set asone cycle T1. In addition, the second drive signal S2 may be asinusoidal wave or the like without limitation to the triangular wave aslong as the second drive signal S2 is an electric signal in which oneswing of the mirror 3 a with respect to the second axial line A2 as acentral line is set as one cycle T2. In addition, in the second signalelement S2 _(i) of the second drive signal S2, the voltage value may notbe constant, and may increase or decrease.

In addition, a circuit that modulates the frequency of the first drivesignal S1 to conform to the resonance frequency of the mirror 3 a may bea DDS (direct digital synthesizer) circuit or the like withoutlimitation to the PLL circuit 51.

The control unit 5 may generate not only the first drive signal S1 inwhich a period varies from the first signal element S1 _(i) in which aperiod varies, but also the first drive signal S1 in which a period isconstant from the first signal element S1 _(i) in which a period isconstant. Even when the control unit 5 generates the first drive signalS1 in which the period is constant from the first signal element S1 _(i)in which the period is constant, a period of the first drive signal S1input to the MEMS mirror mechanism 3 may vary due to a variation of theresonance frequency of the mirror 3 a. Even in this case, according tothe scanning device 1, the first drive signal S1 and the second drivesignal S2 are generated so that m times of reciprocation of theirradiation region of the laser light L1 in the horizontal direction andone time of reciprocation of the irradiation region of the laser lightL1 in the vertical direction correspond to each other.

In addition, the scanning device 1 may be used in various aspects suchas a helmet-embedded type, an eyeglass type without limitation to thevehicle-mounted type. In addition, the scanning device of the presentdisclosure can be used in a distance image sensor. In the distance imagesensor, a distance measurement region is scanned with laser lightemitted from a scanning device, and laser light reflected from thedistance measurement region is detected by a light detector. In thedistance image sensor, a distance is measured with respect to respectivesites in the distance measurement region that is scanned with the laserlight on the basis of time until the laser light is detected with thelight detector after the laser light is pulse-oscillated from a lightsource of the scanning device. A control unit of the scanning devicewhich is used in the distance image sensor generates a first drivesignal and a second drive signal so that m times of reciprocation (m: aninteger of two or greater) of an irradiation region of the laser lightin the first direction and one time of reciprocation of the irradiationregion of the laser light in the second direction correspond to eachother.

REFERENCE SIGNS LIST

1: scanning device, 2: light source, 3: MEMS mirror mechanism, 3 a:mirror, 5: control unit, 31: first movable unit, 32: second movableunit, 33: support unit, 34: first drive coil, 35: second drive coil(drive coil), 36: electromotive force monitoring coil, 37: magnet, A1:first axial line, A2: second axial line, D1: horizontal direction (firstdirection), D2: vertical direction (second direction), L1: laser light.

The invention claimed is:
 1. A scanning device comprising: a lightsource configured to emit laser light; an MEMS mirror mechanismincluding a mirror configured to reflect the laser light emitted fromthe light source, the MEMS mirror mechanism being configured toreciprocate an irradiation region of the laser light in a firstdirection by swinging the mirror with respect to a first axial line as acentral line, and reciprocate the irradiation region in a seconddirection that intersects the first direction by swinging the mirrorwith respect to a second axial line as a central line that intersectsthe first axial line; and a control unit configured to generate a firstdrive signal for swinging the mirror with respect to the first axialline as a central line and a second drive signal for swinging the mirrorwith respect to the second axial line as a central line, and input thefirst drive signal and the second drive signal to the MEMS mirrormechanism, wherein the first drive signal is an electric signal forresonating the mirror in which one swing of the mirror with respect tothe first axial line as a central line is set as one cycle, the seconddrive signal is an electric signal for linearly operating the mirror inwhich one swing of the mirror with respect to the second axial line as acentral line is set as one cycle, and the control unit is configured: tomodulate a frequency of the first drive signal to conform to a resonancefrequency of the mirror; and to generate a second signal elementconstituting the second drive signal so that the second signal elementcorresponds to a first signal element corresponding to a period equal toor less than one cycle period in the first drive signal to generate thefirst drive signal and the second drive signal.
 2. The scanning deviceaccording to claim 1, wherein the control unit is configured to repeatgeneration of the second signal element in both an outgoing period andan incoming period in the one swing of the mirror with respect to thesecond axial line as a central line to generate the first drive signaland the second drive signal so that m times of reciprocation (m: aninteger of two or greater) of the irradiation region in the firstdirection and one time of reciprocation of the irradiation region in thesecond direction correspond to each other.
 3. The scanning deviceaccording to claim 1, wherein the control unit is configured to repeatgeneration of the second signal element in a lighting-on period in anoutgoing period or an incoming period in the one swing of the mirrorwith respect to the second axial line as a central line to generate thefirst drive signal and the second drive signal.
 4. The scanning deviceaccording to claim 1, wherein the control unit is configured to controlthe light source so that the outgoing period corresponds to alighting-on period and the incoming period corresponds to a lighting-offperiod, and repeats generation of the second signal element in both thelighting-on period and the lighting-off period.
 5. The scanning deviceaccording to claim 1, wherein the control unit is configured to controlthe light source so that the outgoing period corresponds to a firstlighting-on period and the incoming period corresponds to a secondlighting-on period, and repeats generation of the second signal elementin both the first lighting-on period and the second lighting-on period.6. The scanning device according to claim 1, wherein the control unit isconfigured to generate the second signal element to correspond to thefirst signal element in a ½ cycle period in the first drive signal. 7.The scanning device according to claim 1, wherein the control unit isconfigured to generate the second signal element to correspond to thefirst signal element in a one cycle period in the first drive signal. 8.The scanning device according to claim 1, wherein the control unit isconfigured to generate the second signal element to correspond to thefirst signal element in a current one cycle period in the first drivesignal.
 9. The scanning device according to claim 1, wherein the controlunit is configured to generate the second signal element to correspondto the first signal element in an immediately previous one cycle periodin the first drive signal.
 10. The scanning device according to claim 1,wherein the MEMS mirror mechanism includes: a first movable unitprovided with the mirror; a second movable unit configured to supportthe first movable unit to be swingable with respect to the first axialline as a central line; a support unit configured to support the secondmovable unit to be swingable with respect to the second axial line as acentral line; a drive coil that is provided in the second movable unit;and a magnet configured to generate a magnetic field acting on the drivecoil.
 11. The scanning device according to claim 1, wherein the lightsource is configured to emit the laser light for projection display, andthe control unit is configured to generate the first drive signal andthe second drive signal so that an image of one frame or two frames isformed by the m times of reciprocation of the irradiation region in thefirst direction and the one time of reciprocation of the irradiationregion in the second direction.
 12. The scanning device according toclaim 11, wherein the control unit is configured to control the lightsource so that the laser light is modulated in correspondence with aposition of the irradiation region.
 13. The scanning device according toclaim 11, wherein the control unit is configured to repeat generation ofthe second signal element while fluctuating a frame rate.